An infrastructure-based wireless network typically includes a communication network with fixed and wired gateways. Many infrastructure-based wireless networks employ a mobile unit or host which communicates with a fixed base station that is coupled to a wired network. The mobile unit can move geographically while it is communicating over a wireless link to the base station. When the mobile unit moves out of range of one base station, it may connect or “handover” to a new base station and starts communicating with the wired network through the new base station.
In comparison to infrastructure-based wireless networks, such as cellular networks or satellite networks, ad hoc networks are self-forming networks which can operate in the absence of any fixed infrastructure, and in some cases the ad hoc network is formed entirely of mobile nodes. An ad hoc network typically includes a number of geographically-distributed, potentially mobile units, sometimes referred to as “nodes,” which are wirelessly connected to each other by one or more links (e.g., radio frequency communication channels). The nodes can communicate with each other over a wireless media without the support of an infrastructure-based or wired network. Links or connections between these nodes can change dynamically in an arbitrary manner as existing nodes move within the ad hoc network, as new nodes join or enter the ad hoc network, or as existing nodes leave or exit the ad hoc network.
One characteristic of the nodes is that each node can directly communicate over a short range with nodes which are a single “hop” away. Such nodes are sometimes referred to as “neighbor nodes.” When a node transmits packets to a destination node and the nodes are separated by more than one hop (e.g., the distance between two nodes exceeds the radio transmission range of the nodes, or a physical barrier is present between the nodes), the packets can be relayed via intermediate nodes (“multi-hopping”) until the packets reach the destination node. In such situations, each intermediate node routes the packets (e.g., data and control information) to the next node along the route, until the packets reach their final destination. For relaying packets to the next node, each node maintains routing information collected through communication with neighboring nodes. The routing information can also be periodically broadcast in the network to reflect the current network topology. Alternatively, to reduce the amount of information transmitted for maintaining accurate routing information, the network nodes may exchange routing information only when it is needed. In an approach known as Mesh Scalable Routing (MSR), nodes periodically send HELLO messages (e.g., once per second) that contain routing information and metrics associated with each route. Mobile nodes use information extracted from the HELLO messages to decide the most efficient manner for performing handoff.
A wireless mesh network is a collection of wireless nodes or devices organized in a decentralized manner to provide range extension by allowing radios to be reached across multiple hops. In a multi hop network, communication packets sent by a source node are relayed through one or more intermediary nodes before reaching a destination node.
A large network can be realized by using infrastructure nodes intelligent access points (IAP), which provides wired backhaul to the wireless nodes. Multiple IAP can be connected to the same local area network (LAN) segment to provide wired backhaul.
Wireless adhoc networks can include both routable (meshed) nodes and non-routable (non-meshed) nodes. Meshed devices are devices which may follow a standard wireless protocol such as IEEE 802.11 or IEEE 802.15. These devices are responsible for forwarding packets to/from the proxy devices which are associated with them. Non-meshed devices are devices following a standard wireless protocol such as IEEE 802.11 or IEEE 802.15 but not participating in any kind of routing. These devices are “proxied” by meshed devices, which establish routes for them.
The mobility of a multihop ad hoc wireless network causes groupcast operations (i.e. broadcast and multicast communication) to occur more frequently than in other communication networks. The purpose of groupcasting a message is to make sure that the groupcast reaches all nodes of interest in the network and is not unnecessarily dropped. Due to the mobile nature of the ad hoc network, groupcasting of messages can cause network problems including redundancy, contention, and collision. Together, these type of issues are referred to by those skilled in the art as a “broadcast storm” problem. In the worst case scenario, a broadcast storm may shut down an entire network.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.